Stages of labour

The early preparation (prelabour phase) goes on for days and weeks, while the onset of painful uterine contractions and delivery is shorter and the process is called parturition or labour. The cervix ripens by becoming softer, shorter and dilating, which takes a greater speed with onset of uterine contractions.

For purposes of clinical management, ‘observed’ labour is a continuum that is divided into three stages:

Onset of labour

It is often difficult to be certain of the exact time of onset of labour because contractions may be irregular and may start and stop with no cervical change, i.e. ‘false labour’. The duration of labour for management purposes is based on the observed progress of the contractions and cervical changes along with the descent of the head. This concept may have to be judged based on the place of practice, as in some remote areas a mother may be brought in after a day of labour with no progress. Her general condition and findings of the maternal and fetal conditions should dictate management. In the rare cases of cervical stenosis that can occur after surgery to the cervix, normal contractions of labour may produce thinning of the cervix without cervical dilatation.

The clinical signs of the onset of labour are:

Uterine activity in labour: the powers

The uterus exhibits infrequent, low-intensity contractions throughout pregnancy. As full term approaches, uterine activity increases in frequency, duration and strength of contractions. By palpation or external tocography one can identify the frequency and duration of contractions, but intrauterine pressure catheters are needed to assess the strength of contractions. It is likely that labour is established if two contractions each lasting for >20 seconds are observed in 10 minutes. Normal resting tonus in labour starts at around 10–20 mmHg and increases slightly during the course of labour (Fig 11.1). Contractions increase in intensity with progress of labour which in some ways are characterized by the duration of contractions. WHO recommends contraction recording on the partograph based on the frequency and duration of contractions.

Progressive uterine contractions cause effacement and dilatation of the cervix as the result of shortening of myometrial fibres in the upper uterine segment and stretching and thinning of the lower uterine segment (Fig. 11.2). This process is known as retraction. The lower segment becomes elongated and thinned as labour progresses and the junction between the upper and lower segment rises in the abdomen. Where labour becomes obstructed, the junction of the upper and lower segments may become visible at the level of the umbilicus; this is known as a retraction ring (also known as Bandl’s ring).

A pacemaker for the uterus has never been demonstrated by anatomical, pharmacological, electrical or physiological studies. The electrical contraction impulse starts in one or the other uterine fundal region and spreads downwards through the myometrium. Contractions are stronger and last longer in the fundus and upper segment than in the lower segment. This fundal dominance is essential for progressive effacement and dilatation of the cervix. As the uterus and the round ligaments contract, the axis of the uterus straightens and pulls the longitudinal axis of the fetus towards the anterior abdominal wall in line with the inlet of the true pelvis.

The realignment of the uterine axis promotes descent of the presenting part as the fetus is pushed directly downwards into the pelvic cavity (Fig. 11.3).

The passages

The shape and structure of the bony pelvis has already been described (see Chapter 6). The size and shape of the pelvis vary from woman to woman and not all women have a gynaecoid pelvis; some may have platypelloid, anthropoid or android pelvis thus influencing the outcome of labour. Softening of the sacroiliac ligaments and the pubic symphysis allow expansion of the pelvic cavity, and this feature along with the dynamic changes of the head diameter brought about by flexion, rotation and moulding facilitate normal progress and spontaneous vaginal delivery.

The soft tissues of the pelvis are more distensible than in the non-pregnant state. Substantial distension of the pelvic floor and vaginal orifice occurs during the descent and birth of the head. The distensible nature of the pelvic soft tissues, vagina and perineum help to reduce the risk of tearing of the perineum and vaginal walls during descent and birth of the head.

The mechanism of labour

The pelvic inlet offers a larger lateral than an anteroposterior diameter. This promotes the head to normally engage in the pelvis in the transverse position. The passage of the head and trunk through the pelvis follows a well-defined pattern because the upper pelvic strait is transverse, the middle pelvic strait is circular and the outer pelvic strait is anteroposterior. The fetal head presents by the vertex in 95% of the cases and hence is called normal presentation. With the vertex presentation the head is well flexed in 90% of the cases and the head rotates to an occipitoanterior position and presents the shortest diameters, i.e. anteroposterior suboccipito bregmatic (9.5 cm) and lateral biparietal (9.5 cm) diameters, hence occipitoanterior position where the occiput is in the anterior half of the pelvis is called normal position. A deflexed or extended head presents as an occipitoposterior or transverse position and with further extension as a brow or face presentation. Labour with an occipitoposterior position is prolonged as a larger anteroposterior diameter of occipitobregmatic or occipitofrontal diameter (11.5 cm) presents to the pelvis. With the brow presentation, entry of the head into the pelvic brim is difficult as it presents the largest anteroposterior–mento vertical diameter (13.5 cm). The brow presentation can flex to a vertex or extend to a face presentation. If there is no progress the baby is best delivered by caesarean section in a term brow presentation.

The process of normal labour therefore involves the adaptation of the fetal head to the various segments and diameters of the maternal pelvis and the following processes occur (Fig. 11.4):

The third stage of labour

The third stage of labour starts with the completed expulsion of the baby and ends with the delivery of the placenta and membranes (Fig. 11.5).

Once the baby is delivered, the uterine muscle contracts, shearing off the placenta and pushing it into the lower segment and the vault of the vagina.

The classic signs of placental separation include trickling of bright blood, lengthening of the umbilical cord and elevation of the uterine fundus within the abdominal cavity. The uterine fundus becomes firm to hard and smaller and rounded instead of being broad and globular and sits on top of the placenta as it descends into the lower segment.

The duration of placental separation may be compressed by the use of oxytocic drugs administered at the delivery of the anterior shoulder.

As the placenta is expelled, it is accompanied by the fetal membranes, although the membranes often become torn and may require additional traction by using a sponge forceps to grasp them. Uterine exploration is rarely needed to complete their removal.

The whole process lasts between 5 and 10 minutes. If the placenta is not expelled within 30 minutes, a diagnosis of retained placenta is made and the third stage should be considered to be abnormal.

Most complications of labour and delivery such as postpartum haemorrhage, pelvic or perineal haematoma and any deterioration of the maternal or newborn condition takes place within the first few hours of delivery and hence in most settings the mother and baby are closely examined with periodic observations in the delivery unit for up to 2 hours before the mother and baby are sent to the postnatal ward. The observations are continued for 6 hours if the mother is to be discharged home from the delivery unit.

Pain in labour

Contractions in labour are invariably associated with pain, particularly as they increase in strength, frequency and duration with progress of labour. The cause of pain is uncertain but it may be due to compression of nerve fibres in the cervical zone or to hypoxia of compressed muscle cells. Pain is felt in the lower abdomen and as lumbar backache when the intrauterine pressure exceeds 25 mmHg.

The management of normal labour

The primary aim of intrapartum care is to deliver a healthy baby to a healthy mother. The preparation of the mother for the process of parturition begins well before the onset of labour. It is important for the mother and her partner to understand what actually happens during the various stages of labour. Strategies to deal with pain in labour, including mental preparation with controlled respiration, should be introduced during antenatal classes, as well as educating the mother about the regulation of expulsive efforts during the second stage of labour.

Antenatal classes should also include instructions about neonatal care and breastfeeding, although this is a process that requires reinforcement in the postdelivery period.

The mother should be advised to come into hospital, or to call the midwife in the event of a home birth, when contractions are at regular 10–15 minute intervals, when there is a show or if and when the membranes rupture. If the mother is in early labour, she should be encouraged to take a shower and to empty her bowels and bladder. Shaving of the pubic hair or abdomen is no longer considered necessary and is likely to cause abrasions with some bleeding that may become the nidus for bacterial proliferation and subsequent infection.

The home birth rate in the UK is about 2–3% but it is common practice to organize ‘domino’ (domiciliary in and out) deliveries, whereby the mother is discharged home 6 hours after delivery, provided that the delivery is uncomplicated.

General principles of the management of the first stage of labour

The guiding principles of management are:

• Observation of the progress of labour and intervention if it is slow.

• Monitoring the fetal and maternal condition.

• Pain relief during labour and emotional support for the mother.

• Adequate hydration and nutrition throughout labour.

Observation: the use of the partogram

The introduction of graphic records of progress of cervical dilatation and descent of the head was a major advance in the management of labour. It enables the early recognition of a labour that is non-progressive. The partogram (Fig. 11.6) is a single sheet of paper on which there is a graphic representation of progress in labour. On the same sheet other observations related to labour can be entered. There are sections to enter the frequency and duration of contractions, fetal heart rate (FHR), colour of liquor, caput and moulding, station or descent of the head, maternal heart rate, BP and temperature. The partogram should be started as soon as the mother is admitted to the delivery suite and this is recorded as zero time regardless of the time at which contractions started. However, the point of entry on to the partogram depends on a vaginal assessment at the time of admission to the delivery suite. The value of this type of record system is that it draws attention visually to any aberration from normal progress in labour.

The use of partograms at an applied level was first introduced in remote obstetric units in Africa, where recognition that progress in labour is becoming abnormal enables early transfer to specialist units before serious obstruction occurs.

This has led to a major reduction in maternal mortality due to avoidance of uterine rupture, sepsis and postpartum haemorrhage and reduction in severe morbidity of vesico or recto vaginal fistula. Earlier recognition of obstructed labours and immediate attention by caesarean delivery where indicated prevents such tragedies.

Fetal condition

The fetal heart rate is charted as beats/min and decelerations of heart rate that occur during contractions are recorded by an arrow down to the lowest heart rate recorded on the partogram. These records are an adjunct to the actual recording of auscultated FHR in the notes and/or electronic fetal monitoring (EFM) by continuous cardiotocography (CTG).

The time of rupture of the membranes and the nature of the amniotic fluid, i.e. whether it is clear or meconium-stained, are also recorded. Moulding of the fetal head and the presence of caput are also noted as they provide an indicator of obstructed labour. The suture lines meeting is moulding +, over riding but reducible with gentle pressure is ++, and overriding and not reducible with gentle pressure is +++. The soft tissue swelling of the scalp called caput is also marked from + to +++ but is based on relative impression formed by the clinician.

Progress in labour

Progress in labour is measured by assessing the rate of cervical dilatation and descent of the presenting part. The progress is assessed by vaginal examination on admission and every 3 to 4 hours afterwards during the first stage of labour. Cervical dilatation is plotted in cm along the scale of 0–10 of the cervicograph. The cervix is expected to efface and dilate from 0 to 3 cm (latent phase) in 6 hours in a multipara and 8 hours in a nullipara, followed by approximately 1 cm per hour from 3 to 10 cm dilatation (active phase) in nulli and multipara although multipara tend to dilate faster. The expected progress recorded on the chart at a rate of 1 cm per hour from admission dilatation in the active phase of labour is called the alert line which helps to identify those who are progressing slowly. A line 2 hours parallel with the alert line called the action line can be drawn to decide on when to actively intervene with artificial rupture of membranes or oxytocin infusion to augment labour in the absence of malpresentation, disproportion or concern for fetal condition.

If the progress of cervical dilatation lags more than 2 hours behind the expected rate of dilatation, it will cut the action line indicating the poor progress in the active phase of labour. The UK National Institute for Health and Clinical Excellence guidelines suggest that when encountered with slow progress of <1 cm in 3 hours with no other changes such as cervical effacement or descent of the head in the presence of ruptured membranes, cephalopelvic disproportion should be excluded and labour augmented with an oxytocin infusion. Descent of the station of the head is charted on the partogram based on the palpable portion of the head above the pelvic brim in fifths, i.e. whether it needs 5, 4, 3, 2 or 1 finger to cover the head.

The station of the head is plotted on the 0–5 gradation of the partogram.

Descent is also recorded by assessing the level of the presenting part in cm above or below the level of the ischial spines and marked as −1, −2, and −3 when it is above the spines and +1, +2, and +3 if it is below the spines.

The nature and frequency of the uterine contractions are recorded on the chart by shading in the number of contractions per 10 minutes. Dotted squares indicate contractions of less than 20 seconds duration, cross-hatched squares are contractions between 20 and 40 seconds duration, while contractions lasting longer than 40 seconds are shown by complete shading of the squares. Frequency and duration of contractions can be measured by clinical palpation or external tocography. The intensity of contractions cannot be assessed by the degree of pain felt by the mother or by palpating the uterus abdominally and can only be determined by intrauterine pressure catheters. However intrauterine catheters are not used routinely in management of labour because their use has been shown not to improve the outcome of labour.

Fluid and nutrition during labour

In most maternity units in the developed world, caesarean section rates now exceed 20%. The issue of what can be taken by mouth therefore becomes particularly important. If there is a likelihood that the mother will need operative delivery under general anaesthesia, then it is clearly important to avoid oral intake at any significant level during the first stage of labour. Delayed gastric emptying may result in vomiting and inhalation of vomitus if general anaesthesia for operative delivery is needed. On the other hand, most operative deliveries are now achieved under regional anaesthesia and therefore there is a case for giving some fluids and light nutrition orally if labour is progressing normally and a vaginal delivery can be anticipated. Recent clinical trials have suggested little concern with feeding the mother with soft easily digestible solid nutrition in addition to fluids. Intravenous fluid replacement should be considered after 6 hours in labour if delivery is not imminent. The major cause of acidosis and ketosis is dehydration, and urine should be checked for ketones in addition to sugar and protein whenever mother passes urine. Administration of normal saline or Hartmann’s solution is preferred and the fluid input and output should be monitored not to over or under hydrate the mother.

The classic signs of dehydration in labour include tachycardia, mild pyrexia and loss of tissue turgor. Remember that labour can be hard physical work and that the environmental temperature of delivery rooms is often raised to meet the needs of the baby rather than the mother, leading to considerable insensible fluid loss.

Pain relief in labour

There are a number of strategies used in labour for the relief of pain and these should be discussed with the pregnant mother in the antenatal period. Essentially, these techniques are aimed at reducing the level of pain experienced in labour whilst invoking minimal risk for the mother and baby.

The level of pain experienced in labour varies widely, some experience very little whilst others suffer from abdominal and back pain of increasing intensity throughout their labour. Thus, any programme for pain relief must be tailored to the needs of the individual. The care giver may be able to advise the best mode of pain relief based on whether the mother is nulliparous or multiparous, the current cervical dilatation, the rate of progress of labour and the extent to which the mother is feeling the pain. The mode of pain relief is best decided by the mother based on the advice given. Often this may result in a combination of methods, starting from the least to most effective method to alleviate her pain. The only technique that can provide complete pain relief is epidural analgesia.

Regional analgesia

Epidural analgesia is the most effective and widely used form of regional analgesia. It provides complete relief of pain in 95% of labouring women.

The procedure may be instituted at any time and does not interfere with uterine contractility. It may reduce the desire to bear down in the second stage of labour due to lack of pressure sensation at the perineum and reduced uterine activity due to loss of ‘Ferguson reflex’: which is an increased uterine activity due to reflex release of oxytocin due to the presenting part stretching the cervix and upper vagina.

A fine catheter is introduced into the lumbar epidural space and a local anaesthetic agent such as bupivacaine is injected (Fig. 11.7). The addition of an opioid to the local anaesthetic greatly reduces the dose requirement of bupivacaine, thus sparing the motor fibres to the lower limbs and reducing the classic complications of hypotension and abnormal fetal heart rate.

The procedure involves:

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